1. Field of the Invention
The present invention relates to a pulse combustor adapted for use in liquid heating apparatuses. More particularly, the invention relates to an ignition control apparatus for the pulse combustor.
2. Description of the Prior Art
A conventional pulse combustor of this kind includes a fuel-air mixer head to be supplied with fresh air from a purge blower and gaseous fuel from a fuel supply pipe. The fuel-air mixture from the mixer head is supplied into a combustion chamber and ignited by energization of a spark electrode for a predetermined period of time. If ignition of the fuel-air mixture is not successfully obtained by the trial for ignition, a predetermined number of trials for ignition are attempted at a predetermined time interval. In general, the time interval of the trials for ignition is defined to cause change of the unburned mixture ratio to a non-combustible ratio under a forced draft of fresh air from the purge blower.
In operation of the pulse combustor, however, the supply amount of forced air from the purge blower will decrease if the air inlet of the mixer head is partly closed by foreign particles adhered thereto or the exhaust flow of combustion products is obstructed by soot collected in the exhaust passage of the combustion chamber. This results in insufficient pre-purge of the unburned mixture from an exhaust decoupler connected to the combustion chamber through a tailpipe. If the predetermined number of trials for ignition are attempted before the unburned mixture ratio is changed to a non-combustible ratio, the user will be surprised at explosive noise caused by instant combustion of the unburned mixture in the decoupler on the trial for ignition.
To solve such problems as described above, there has been proposed an ignition control apparatus for the pulse combustor wherein a pressure switch is provided to detect the supply quantity of forced air from the purge blower thereby to deactivate the pulse combustor when the supply quantity of forced air has decreased below a predetermined value. The pressure switch is, however, expensive because of high precision required thereto, resulting in an increase of manufacturing cost of the pulse combustor.